Process for reducing the odor of vinylaromatic-1,3-diene copolymer dispersions stabilized by protective colloids

ABSTRACT

The invention relates to a method for reducing odor emissions of aqueous aromatic vinyl-1,3-diene-copolymer dispersions which have been stabilized with a protective colloid. The invention also relates to redispersion powders obtained by drying said dispersions. This is achieved by emulsion polymerization of a mixture containing at least one aromatic vinyl and at least one 1,3-diene in the presence of one or more protective colloids and by optionally drying the polymer dispersion obtained thereby. The invention is characterized in that 0.01 to 15.0 wt. % of one or more monomers selected from the group of branched or unbranched alkyl esters containing 1 to 8 carbon atoms in the alkyl radical of monounsaturated mono- or dicarboxylic acids are added at the end of the polymerization when the total content of the aqueous polymer dispersion containing free monomers ranges from &gt;0 to ≦20 wt. %, whereby the given wt. % refers to the polymer content of the dispersion.

The invention relates to a process for reducing the odor emission ofaqueous protective-colloid-stabilized vinylaromatic-1,3-diene copolymerdispersions, and also of redispersion powders which are obtainable bydrying polymer dispersions of this type.

Aqueous polymer dispersions based on vinylaromatic-1,3-diene copolymerdispersions and redispersion powders obtainable therefrom, generally byspray drying, are used chiefly in the construction sector as agents forincreasing the quality of finished pulverulent mixtures of cement ornon-cement type. A problem with dispersions and redispersion powders ofthis type is that they generally still comprise volatile high-odorconstituents, e.g. mercaptans which serve as molecular weight regulatorsduring the polymerization, ammonia, which is used for neutralization,residual monomers, non-polymerizable contaminants of the monomers,volatile reaction products formed from the monomers under the conditionsof the reaction, or also volatile degradation products of the polymers.The resultant odor is perceived as unpleasant both by the producers andby the users, and there is therefore a need for deodorized aqueouspolymer dispersions.

It is known that polymer dispersions can be deodorized by physicalchemical post-treatment. An example of a physical process is adistillative process, in particular steam distillation, or strippingusing inert gases, as mentioned, for example, in EP-A 327006. Adisadvantage of this process is that many dispersions do not havesufficient stability for this type of deodorization, and coagulationtherefore occurs, requiring complicated filtration before subsequentuse. Another disadvantage of the process is that although it is capableof reducing the proportion of volatile substances in the aqueous polymerdispersion it does not resolve the issue of disposal of thesesubstances.

It is also known that polymer dispersions can be freed from high-odormonomers by chemical post-treatment. For example, DE-A 4419518 describesa chemical process for lowering the amount of residual monomers byfree-radical post-polymerization with exposure to redox initiatorsystems. U.S. Pat. No. 4,529,753 describes a process in which theresidual monomer content of aqueous polymer dispersions can be reducedby free-radical post-polymerization brought about by particularfree-radical redox initiator systems after the main polymerizationreaction is complete. Redox initiator systems of this type include atleast one oxidant, at least one reducing agent, and one or moretransition metal ions which occur in different valence states.

However, a disadvantage of the processes recommended above is thatalthough they can bring about some reduction of residual monomer contentwhen used in high-odor polymer dispersions, such as styrene-butadienedispersions, they are not able effectively to reduce the unpleasant odorbrought about by styrene and high-odor byproducts, for examplemercaptans, non-polymerizable contaminants of the monomers, volatilereaction products of the monomers or volatile degradation products ofthe polymers.

DE-A 19728997 describes deodorized aqueous polymer dispersionsobtainable by adding the zinc salt of ricinoleic acid and/or the zincsalt of abietic acid or, respectively, analogous resin acids and/orother zinc salts of other saturated or unsaturated hydroxylated fattyacids having 16 or more carbon atoms. A disadvantage of this method,however, is that, due to additional electrolyte loading, it impairs thestability this method, however, is that, due to additional electrolyteloading, it impairs the stability of the aqueous polymer dispersion.

The adsorbing action of adsorbents with respect to volatile organicsubstances is known. WO-A 98/11156 describes a process in which addingeven small amounts (from 0.1 to 20% by weight, based on polymericconstituents of the dispersion) of active carbon in polymer dispersionsbinds the odor-forming volatile contaminants so strongly that these arepractically no longer detectable either in the polymer dispersions or inthe products produced using the polymer dispersions. A disadvantage ofthis process is that the residence time of the active carbon is up totwo more hours for effective odor reduction, and the dispersiongenerally then has to be filtered (in particular for pigmented systems,e.g. emulsion paints) before further use. This is a disadvantage bothfrom an economic point of view and also ecologically, especially sincethe disposal of the contaminated active carbon filtered off is an issuewhich remains open.

EP-A 283348 relates to a process for removing residual monomer, i.e.unreacted acrylonitrile, from acrylonitrile polymer dispersions bypost-polymerization via addition of any desired monomers copolymerizablewith acrylonitrile. In contrast, the object of the present applicationalso includes minimizing the nuisance caused by non-polymerizableodoriferous substances.

Aqueous protective-colloid-stabilized styrene-butadiene polymerdispersions are two-phase systems which are composed of an aqueous phaseand a polymer phase. Both the dispersed polymer particles and theaqueous dispersion medium are locations where high-odor constituents maybe present. Between these two phases a distribution equilibrium becomesestablished. The disadvantage of the known methods for reducing theproportion of volatile constituents in aqueous polymer dispersions is,specifically, that they essentially affect either solely the aqueousdispersion or solely the polymer particles. This means that anysignificant total reduction in the proportion of volatile constituentsin the aqueous polymer dispersion will essentially bediffusion-controlled (reestablishment of the distribution equilibrium)and this is probably the reason for the unsatisfactory rate of reductionin the proportion of volatile odoriferous materials in aqueous polymerdispersions when the known methods are used.

Surprisingly, it has been found that deodorization of the odoriferousmaterials located both in the aqueous phase and the polymer phase takesplace if, toward the end of the main polymerization, esters ofunsaturated carboxylic acids are added to the reaction mixture.

The invention provides a process for reducing the odor emission ofaqueous protective-colloid-stabilized vinylaromatic-1,3-diene copolymerdispersions and of redispersion powders obtainable therefrom by drying,by emulsion polymerization of a mixture comprising at least onevinylaromatic and at least one 1,3-diene in the presence of one or moreprotective colloids and, if desired, drying the resultant polymerdispersion, which comprises, toward the end of the polymerization, whenthe total free monomer content of the aqueous polymer dispersion is from0 to 20% by weight, adding from 0.01 to 15.0% by weight of one or moremonomers selected from the class consisting of branched or unbranchedalkyl esters, having from 1 to 8 carbon atoms in the alkyl radical, ofmonounsaturated mono- or dicarboxylic acids, where the data in % byweight are in each case based on the polymer content of the dispersion.

Preference is given to adding the alkyl esters of acrylic acid,methacrylic acid, fumaric acid, maleic acid or itaconic acid, such asmethyl methacrylate, methyl acrylate, n-butyl methacrylate, n-butylacrylate, ethyl methacrylate, ethyl acrylate, 2-ethylhexyl methacrylate,2-ethylhexyl acrylate, diisopropyl fumarate, diethyl fumarate ormixtures of these. n-Butyl acrylate is particularly preferred.

The alkyl esters mentioned may be added as such or in aqueous emulsion.The amount added is preferably from 0.1 to 5% by weight, based on thepolymer content of the aqueous polymer dispersion. The addition takesplace toward the end of the polymerization, when the total free monomercontent of the aqueous polymer dispersion is from 0 to 20% by weight, inother words the conversion of the entire amount of monomer used is from80 to <100%. The addition preferably takes place when the total freemonomer content of the aqueous dispersion, based on the polymer contentof the dispersion, has fallen to from 5 to 15% by weight, correspondingto a conversion of from 85 to 95%. After adding the alkyl esters thepolymerization is continued until no further monomer conversion can bedetected.

Suitable vinylaromatics are styrene and methylstyrene, and preference isgiven to copolymerizing styrene. Examples of 1,3-dienes are1,3-butadiene and isoprene, preferably 1,3-butadiene. The copolymersgenerally comprise from 20 to 80% of vinylaromatic and from 20 to 80% of1,3-diene and, if desired, other monomers may be present. In each casethe data in percent by weight give 100% by weight in total.

Examples of other monomers are monomers copolymerizable withvinylaromatics and with 1,3-dienes, for example ethylene, vinylchloride, (meth)acrylates of alcohols having from 1 to 15 carbon atomsor vinyl esters of unbranched or branched carboxylic acids having from 1to 15 carbon atoms, of comonomers such as ethylenically unsaturatedmono- and dicarboxylic acids, ethylenically unsaturated carboxamides,ethylenically unsaturated carbonitriles, mono- and diesters of fumaricacid and maleic acid, maleic anhydride, ethylenically unsaturatedsulfonic acids, comonomers with more than one ethylenic unsaturation orpost-crosslinking comonomers, epoxy-functional comonomers, orsilicon-functional comonomers, monomers with hydroxyl or CO groups.Suitable monomers and comonomers are described, for example, in the PCTapplication PCT/EP98/06102, the disclosure of which on this matter isincorporated into this application by way of reference.

Preparation by emulsion polymerization takes place at from 40 to 100°C., preferably from 60 to 90° C. The polymerization is initiated withcommonly used emulsion-polymerization initiators or redox-initiatorcombinations, for example hydroperoxides, such as tert-butylhydroperoxide, azo compounds, such as azobisisobutyronitrile, orinorganic initiators, such as the sodium, potassium and ammonium saltsof peroxodisulfuric acid. The amount used of the initiators mentioned isgenerally from 0.05 to 3% by weight, based on the total weight of themonomers. Redox initiators used are combinations of the initiatorsmentioned with reducing agents, such as sodium sulfite, sodiumhydroxymethanesulfinate, or ascorbic acid. The amount of reducing agentis preferably from 0.01 to 5.0% by weight, based on the total weight ofthe monomers.

The polymerization mixture is stabilized using protective colloids,preferably without additional emulsifiers. Suitable protective colloidsare fully or partially hydrolyzed polyvinyl acetates. Other suitablepolyvinyl acetates are partially hydrolyzed hydrophobicized polyvinylacetates, and the hydrophobicization may, for example, take place bycopolymerizing with isopropenyl acetate, ethylene or vinyl esters ofsaturated alpha-branched monocarboxylic acids having from 5 to 11 carbonatoms. Other examples are polyvinylpyrrolidones; polysaccharides inwater-soluble form, such as starches (amylose and amylopectin),celluloses and carboxymethyl, methyl, hydroxyethyl or hydroxypropylderivatives of these; proteins, such as casein or caseinate or soyaprotein or gelatine; ligninsulfonates; synthetic polymers, such aspoly(meth)acrylic acid, copolymers of (meth)acrylates withcarboxyl-functional comonomer units, poly(meth)acrylamide,polyvinylsulfonic acids and water-soluble copolymers of these;melamine-formaldehyde sulfonates, naphthalene-formaldehyde-sulfonates,styrene-maleic acid copolymers, vinyl ether-maleic acid copolymers anddextrins, such as yellow dextrin.

Preference is given to the partially hydrolyzed polyvinyl acetates andpartially hydrolyzed hydrophobicized polyvinyl acetates mentioned.Particular preference is given to partially hydrolyzed polyvinylacetates with a degree of hydrolysis from 80 to 95 mol % and a Höpplerviscosity (4% strength aqueous solution, DIN 53015, Höppler method at20° C.) of from 1 to 30 mPas, preferably from 2 to 15 mPas.

The total amount of the protective colloids generally used in thepolymerization is from 1 to 15% by weight, based on the total weight ofthe monomers. Some of the protective colloid here is preferably withinthe initial charge and some is fed once the polymerization has beeninitiated. All of the monomers may be within the initial charge, or allmay be fed, or proportions may be within the initial charge and theremainder fed once the polymerization has been initiated. A suitablepreparation process is described, for example, in the PCT applicationPCT/EP98/06102, the disclosure of which in this connection isincorporated into this application by way of reference. The resultantaqueous dispersions have a solids content of from 30 to 75% by weight,preferably from 40 to 65% by weight.

To prepare the water-redispersible polymer powders, the aqueousdispersions are dried, for example by fluidized-bed drying, freezedrying or spray drying. The dispersions are preferably spray dried. Thespray drying here takes place in conventional spray drying systems, andsingle-, two- or multi-fluid nozzles, or a rotating disk, may be usedfor atomization. The discharge temperature chosen is generally from 55to 100° C., preferably from 70 to 90° C., depending on the system, theTg of the resin and the desired degree of drying. The spraying isdescribed in the PCT application PCT/EP98/06102, the disclosure of whichin this connection is incorporated into this application by way ofreference.

Surprisingly, it has been found that the deodorization acts on odoremitters in both the aqueous and the polymer phase of the dispersion.However, it is advantageous that even small amounts of carboxylic esterhave a sufficient deodorizing action, and its addition does nottherefore generally impair the performance properties of the aqueouspolymer dispersion. The stability of distribution of the dispersion andthe suitability of the dispersion for subsequent spray drying are alsonot impaired.

The polymer dispersions, and the dispersion powders prepared therefromby drying, which have reduced odor emission can be used in aconventional manner known to the skilled worker to give industrialproducts, for example as a constituent of the formulation in combinationwith inorganic, hydraulically setting binders in construction adhesives,renders, troweling compositions, floor-filling compositions, jointingmortars, plaster or paints, or also as sole binders for coatingcompositions and adhesives, or also as coating compositions or bindersfor textiles or paper.

The examples listed below are intended to illustrate the invention butnot to restrict the same.

EXAMPLE 1

3.41 l of deionized water and 3.85 kg of a 20% strength aqueous solutionof a partially hydrolyzed polyvinyl acetate with a degree of hydrolysisof 88 mol %, a Höppler viscosity of the 4% strength solution of 4 mPas(DIN 53015, Höppler method at 20° C.) form the initial charge in astirred autoclave of capacity about 16 l. 10% strength by weight formicacid was used to adjust the pH to 4.0-4.2. The system was thenevacuated, flushed with nitrogen and evacuated again, and a mixture of4.56 kg of styrene, 2.45 kg of 1,3-butadiene and 48.1 g of tert-dodecylmercaptan was introduced by suction. After heating to 80° C. thepolymerization was initiated by running in, simultaneously, two catalystsolutions of which the first was composed of 197 g of deionized waterand 66 g of a 40% strength aqueous tert-butyl hydroperoxide solution andthe other of 508 g of deionized water and 57 g of sodiumformaldehyde-sulfoxylate. The feed rate for the peroxide solution was 44ml/h and that for the sodium formaldehyde-sulfoxylate solution was 94ml/h. 3.5 hours after the polymerization had begun the conversion of themonomers forming the initial charge was 87%. At this juncture the feedof 315 g of butyl acrylate began at a rate of 630 g/h. 2 hours after thebutyl acrylate feed had been completed the initiator feeds were stopped,the reactor contents cooled to 50° C. and stirring continued for onehour in vacuo.

This gave a stable, coagulate-free dispersion with an average particlesize (weight average) of 490 nm with a solids content of 49.3% and aviscosity (Brookfield viscometer, 20° C., 20 rpm) of 3200 mPas.

400 parts by weight of the dispersion were admixed with 200 parts byweight of a 10.3% strength by weight solution of a polyvinyl alcohol(partially hydrolyzed polyvinyl acetate, degree of hydrolysis 88 mol %,viscosity of the 4% strength solution: 13 mPas), 0.84 parts by weight ofantifoam and 135 parts by weight of water, and thoroughly mixed. Thedispersion was sprayed through a two-fluid nozzle. The sprayingcomponent used was air compressed to 4 bar, and the droplets formed weredried cocurrently with air heated to 125° C.

The resultant dry powder was admixed with 10% of commercially availableantiblocking agent (mixture of calcium magnesium carbonate and magnesiumhydrosilicate).

EXAMPLE 2

The dispersion was prepared as in Example 1 except that 3.5 hours afterthe polymerization had begun (87% monomer conversion) 315 g of methylacrylate (instead of butyl acrylate) were fed within 30 min.

This gave a stable, coagulate-free dispersion with an average particlesize (weight average) of 512 nm with a solids content of 50.2% and aviscosity (Brookfield viscometer, 20° C., 20 rpm) of 2750 mPas.

All other measures for preparing the dispersion powder were as inExample 1.

EXAMPLE 3

The dispersion was prepared as in Example 1 except that 3.5 hours afterthe polymerization had begun (87% monomer conversion) 315 g of ethylacrylate (instead of butyl acrylate) were fed within 30 min.

This gave a stable, coagulate-free dispersion with an average particlesize (weight average) of 550 nm with a solids content of 50.9% and aviscosity (Brookfield viscometer, 20° C., 20 rpm) of 3950 mPas.

All other measures for preparing the dispersion powder were as inExample 1.

EXAMPLE 4

The dispersion was prepared as in Example 1 except that 3.5 hours afterthe polymerization had begun (87% monomer conversion) 315 g of2-ethylhexyl acrylate (instead of butyl acrylate) were fed within 30min.

This gave a stable, coagulate-free dispersion with an average particlesize (weight average) of 635 nm with a solids content of 51.6%, and aviscosity (Brookfield viscometer, 20° C., 20 rpm) of 3750 mPas.

All other measures for preparing the dispersion powder were as inExample 1.

EXAMPLE 5

The dispersion was prepared as in Example 1 except that 3.5 hours afterthe polymerization had begun (87% monomer conversion) 315 g of methylmethacrylate (instead of butyl acrylate) were fed within 30 min.

This gave a stable, coagulate-free dispersion with an average particlesize (weight average) of 489 nm with a solids content of 52.5% and aviscosity (Brookfield viscometer, 20° C., 20 rpm) of 6450 mPas.

All other measures for preparing the dispersion powder were as inExample 1.

COMPARATIVE EXAMPLE 6

The dispersion was prepared as in Example 1 except that 3.5 hours afterpolymerization had begun (87% monomer conversion). 315 g of acrylic acid(instead of butyl acrylate) were fed within 30 min.

This gave a stable, coagulate-free dispersion with an average particlesize (weight average) of 946 nm with a solids content of 50.5% and aviscosity (Brookfield viscometer, 20° C., 20 rpm) of 1930 mPas.

All other measures for preparing the dispersion powder were as inExample 1.

COMPARATIVE EXAMPLE 7

The dispersion was prepared as in Example 1 except that 3.5 hours afterpolymerization had begun (87% monomer conversion) 315 g of methacrylicacid (instead of butyl acrylate) were fed within 30 min.

This gave a stable, coagulate-free dispersion with an average particlesize (weight average) of 865 nm with a solids content of 51.1% and aviscosity (Brookfield viscometer, 20° C., 20 rpm) of 2450 mPas.

All other measures for preparing the dispersion powder were as inExample 1.

EXAMPLE 8

The dispersion was prepared as in Example 1 except that 3.5 hours afterthe polymerization had begun (87% monomer conversion) 315 g ofdiisopropyl fumarate (instead of butyl acrylate) were fed within 30 min.

This gave a stable, coagulate-free dispersion with an average particlesize (weight average) of 564 nm with a solids content of 51.3%, and aviscosity (Brookfield viscometer, 20° C., 20 rpm) of 4210 mPas.

All other measures for preparing the dispersion powder were as inExample 1.

EXAMPLE 9

The dispersion was prepared as in Example 1 except that 3.5 hours afterthe polymerization had begun (87% monomer conversion) 315 g of diethylfumarate (instead of butyl acrylate) were fed within 30 min.

This gave a stable, coagulate-free dispersion with an average particlesize (weight average) of 652 nm with a solids content of 52.1% and aviscosity (Brookfield viscometer, 20° C., 20 rpm) of 3750 mPas.

All other measures for preparing the dispersion powder were as inExample 1.

COMPARATIVE EXAMPLE 10

The dispersion was prepared as in Example 1 except that 3.5 hours afterpolymerization had begun (87% monomer conversion) 315 g of monoethylfumarate (instead of butyl acrylate) were fed within 30 min.

This gave a stable, coagulate-free dispersion with an average particlesize (weight average) of 856 nm with a solids content of 51.1% and aviscosity (Brookfield viscometer, 20° C., 20 rpm) of 4750 mPas.

All other measures for preparing the dispersion powder were as inExample 1.

COMPARATIVE EXAMPLE 11

The dispersion was prepared as in Example 1 except that no butylacrylate was added.

This gave a stable, coagulate-free dispersion with an average particlesize (weight average) of 489 nm with a solids content of 51.3% and aviscosity (Brookfield viscometer, 20° C., 20 rpm) of 3970 mPas.

All other measures for preparing the dispersion powder were as inExample 1.

Testing of the Polymer Powders

Evaluation of odor on dispersion films of redispersions of thedispersion powders.

To produce the films a dispersion of about 30% strength was produced byredispersion in water of the dispersion powders prepared. The referencesubstance used was a 30% strength aqueous redispersion of the dispersionpowder from the comparative example.

To produce films the dispersions were poured onto a sheet of siliconerubber and then dried for 24 hours at 23° C. The resultant films ofdimensions 15×10 cm were placed into a 250 ml wide-necked glass bottle,preheated to 75° C. and having a screw top, and placed for 5 minutes ina drying cabinet heated to 75° C. The samples were then allowed to coolto room temperature, and the odor was evaluated by eight test personnelusing a scale of grades from 1 to 6 (odor intensity). The odor testresults are given in Table 1:

TABLE 1 Odor test results Example 1 2 3 4 5 C6 C7 8 9 C10 C11 Intensity=> Tester 1 1 4 2 1 3 4 3 3 3 5 6 Tester 2 2 3 3 2 2 5 3 3 3 6 6 Tester3 1 3 2 2 3 5 4 1 4 4 6 Tester 4 1 4 4 1 4 2 3 3 3 5 5 Tester 5 1 5 2 33 6 5 2 4 6 6 Tester 6 2 3 3 1 2 5 3 1 2 4 4 Tester 7 1 2 2 2 3 4 3 2 45 6 Tester 8 2 5 3 1 2 3 4 3 3 4 6

The results in Table 1 show that when the novel procedure is used todeodorize polymer dispersions and dispersion powders the result is amarked reduction in undesirable odor.

Determination of sedimentation behavior of the powders (tubesedimentation):

To determine sedimentation behavior, 50 g of each dispersion powder wereredispersed in 50 ml of water, then diluted to 0.5% solids content, andthe height of settled solids is measured for 100 ml of this redispersionpoured into a graduated tube, settlement being measured after 1 hour and24 hours. The results of the test are given in Table 2.

Determination of blocking resistance:

To determine blocking resistance, the dispersion powder was placed in aniron tube with a thread, and then subjected to a load from a metal ram.The application of the load was followed by storage for 16 hours at 50°C. in a drying cabinet. After cooling to room temperature, the powderwas removed from the tube and resistance to blocking was determinedqualitatively by crushing the powder. Resistance to blocking wasclassified as follows:

1=very good blocking resistance

2=good blocking resistance

3=satisfactory blocking resistance

4=not resistant to blocking, powder after crushing no longerfree-flowing.

The test results are given in Table 2.

TABLE 2 Tube sedimentation Example 1 h/24 h [cm] Blocking resistance 10.1/0.5 1 2 0.1/0.6 1 3 0.2/0.8 2 4 0.6/1.3 3 5 0.2/0.6 1 C 6 0.1/0.3 2C 7 0.1/0.4 1 8 0.5/0.9 2 9 0.6/1.3 2  C 10 0.3/0.9 2  C 11 0.1/0.5 1

The results in Table 2 show that the deodorizing treatment does notgenerally cause any concomitant loss of powder quality.

What is claimed is:
 1. In a process for preparation of aqueousprotective-colloid-stabilized vinylaromatic-1,3-diene copolymerdispersions and redispersible powders obtainable therefrom by drying,said copolymer dispersions prepared by emulsion polymerizing a mixturecomprising at least one vinylaromatic monomer and at least one 1,3-dienemonomer in the presence of at least one protective colloid and, forredispersible powders, drying the resultant polymer dispersion, theimprovement comprising reducing the odor of said copolymer dispersion byadding to the terminal portion of the polymerization, when the totalfree monomer content of the aqueous polymer dispersion is from 0 to 20%by weight, from 0.01 to 15.0% by weight of one or more branched orunbranched C₁₋₈ alkyl esters of monounsaturated mono- or dicarboxylicacids as odor-reducing monomers, where the percents by weight are ineach case based on the polymer content of the dispersion.
 2. The processof claim 1, wherein one or more alkyl esters of acrylic acid,methacrylic acid, fumaric acid, maleic acid or itaconic acid are saidodor-reducing monomers.
 3. The process of claim 1, wherein one or moreesters selected from methyl methacrylate, methyl acrylate, n-butylmethacrylate, n-butyl acrylate, ethyl methacrylate, ethyl acrylate,2-ethylhexyl methacrylate, 2-ethylhexyl acrylate, diisopropyl fumarateand diethyl fumarate are added to said polymerization.
 4. The process ofclaim 1, wherein 20 to 80% by weight of styrene and from 20 to 80% byweight of 1,3-butadiene are copolymerized, optionally in the presence ofadditional monomers other than said odor-reducing monomers.
 5. Theprocess of claim 2, wherein 20 to 80% by weight of styrene and from 20to 80% by weight of 1,3-butadiene are copolymerized, optionally in thepresence of additional monomers other than said odor-reducing monomers.6. The process of claim 3, wherein 20 to 80% by weight of styrene andfrom 20 to 80% by weight of 1,3-butadiene are copolymerized, optionallyin the presence of other monomers other than said odor-reducingmonomers.
 7. An aqueous, protective-colloid-stabilizedvinylaromatic-1,3diene copolymer dispersion with reduced odor emissionprepared by the process of claim
 2. 8. An aqueous,protective-colloid-stabilized vinylaromatic-1,3-diene copolymerdispersion with reduced odor emission prepared by the process of claim3.
 9. An aqueous, protective-colloid-stabilized vinylaromatic-1,3-dienecopolymer dispersion with reduced odor emission prepared by the processof claim
 3. 10. An aqueous, protective-colloid-stabilizedvinylaromatic-1,3-diene copolymer dispersion with reduced odor emissionprepared by the process of claim
 4. 11. A redispersibleprotective-colloid-stabilized vinylaromatic-1,3-diene copolymer powderprepared by the process of claim
 1. 12. A redispersibleprotective-colloid-stabilized vinylaromatic-1,3-diene copolymer powderprepared by the process of claim
 2. 13. A redispersibleprotective-colloid-stabilized vinylaromatic-1,3-diene copolymer powderprepared by the process of claim
 4. 14. In an inorganic, hydraulicallysetting binder in a construction adhesive, a render, a trowelingcompositions, a floor-filling composition, a jointing mortar, a plasteror a paint, wherein a polymer dispersion or redispersible polymer powderis employed, the improvement comprising employing as said polymerdispersion and/or said redispersible polymer powder a low odor polymerdispersion or redispersible powder prepared by the process of claim 1.15. In a coating composition employing a binder, the improvementcomprising employing as the sole binder, a low odor polymer dispersionor redispersible powder prepared by the process of claim
 1. 16. In anadhesive wherein a polymer dispersion or redispersible polymer powder isemployed, the improvement comprising employing as said polymerdispersion and/or said redispersible polymer powder a low odor polymerdispersion or redispersible powder prepared by the process of claim 1.17. In a coating composition or binder for textiles or paper, wherein apolymer dispersion or redispersible polymer powder is employed, theimprovement comprising employing as said polymer dispersion and/or saidredispersible polymer powder a low odor polymer dispersion orredispersible powder prepared by the process of claim 1.